1. Field of the Invention
The present invention concerns a process for correcting the output level of a charge-transfer device, as well as a device for operating the same.
This correction process, which consists in equalizing the output level of a charge-transfer device for uniform input signals, can be used on any charge-transfer device. It is, however more particularly interesting when the charge-transfer device is used for multiplexing photodiodes, especially in the infrared field. Indeed, in this case the photodiodes are formed of materials such as cadmium and mercury telluride, tin and lead telluride or indium antimonide. However, with these types of materials, it is difficult to obtain photodiodes all presenting the same characteristics. This means that the photodiodes have responses to lighting that are very often inhomogeneous. Since these inhomogeneities are much higher than the minimum response deviation that it is desired to be able to detect on photodiodes, their compensation is thus essential. Among these inhomogeneities, one of them concerns the output level that can be observed when the photodiodes are illuminated by an uniform temperature scene.
2. Description of the Prior Art
Different processes have been used to correct this type of inhomogeneities. According to a process of the prior art, in a first step the photodiodes are illuminated with an uniform temperature scene or reference background. The data read at the output of the charge-transfer device used for the multiplexing of the photodiodes, is sent after digital conversion into a memory in which, for each stage of the charge-transfer device, data corresponding to the inhomogeneities is stored. In a second step, the photodiodes are illuminated by the scene to be observed. The data read in the output of the charge-transfer device is sent to a subtractor through which is corrected the output signal corresponding to each photodiode by subtracting the corresponding inhomogeneity value stored in the memory after it has been reconverted into an analogical form through the intermediary of a digital-to-analogue converter.